The experiments described herein are designed to evaluate the biological role of the hepatic microsomal hydroperoxide peroxidase. Its activity will be distinguished from the other microsomal enzyme activities, especially from the mixed function oxidase (MFO) system. Experiments to separate these activities will include using specific metabolic inhibitors, antibody inhibitors, comparative induction using phenobarbital, 3-methylcholanthrene and lipid hydroperoxide (oleic acid hydroperoxide). The microsomal membrane has been solubilized using the anionic detergent, Emulgen 911. Separation of the enzymes and cytochromes has been accomplished using column chromatography (DEAE, CMC, AND ULTRAGEL). Purification of each fraction will be based on specific activity and SDS-polyacrylamide electrophoresis. Recombination of these fractions in the presence of lipids extracted from the microsomal membrane will be used to prove their viability in regaining the MFO activity. Then omitting the cytochrome P450, the peroxidase activity will be examined using recombination of various fractions. This will allow evaluation for an undefined factor in the peroxidase activity. In addition, a new NADPH cytochrome b5 reductase has been separated. Further characterization of it in the various microsomal activities will be examined. Finally, participation of the peroxidase in maternal, placental, fetal and newborn rat xenobiotic metabolism will be examined.